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OpenTherm Regulator

Open-source Arduino compatible heating regulator to give you ultimate control and monitoring over your heating system

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OpenTherm Regulator is an open-source Arduino compatible heating regulator. It gives you total freedom over your heating system with or without OpenTherm boiler and thermostat. You can use it as a monitor/remote control for your boiler or as a regulator for a complex heating system. It will probably match the capabilities of industry grade devices on the market. Check out the many features:

Features:
- Arduino compatible (MicroChip ATmega2561 microcontroller)
- built-in OpenTherm support - can act as a master, slave or gateway to boiler and thermostat
- 6 NTC temperature sensors (1 built-in) to monitor temperatures on various pipes and tanks
- water pressure sensor
- 3 high voltage relays to control pumps or boiler
- 3-way valve actuator control output
- Real-time clock
- ethernet connectivity
- WiFi connectivity
- NRF connectivity
- large display and rotary encoder as user interface
- 24V power supply (5V if OpenTherm is not used)

History

It all started a year ago when I installed a fireplace with an accumulator tank into my house as an addition to OpenTherm gas boiler. Instantly I had to solve a problem - how do I force my heating system to use hot water from accumulator tank if there is any instead of firing up a gas boiler. Solutions are many, but either too uncomfortable or too expensive. In the same time, I wanted to keep the current gas boiler and its intelligent remote controller. I decided to build my own Arduino based device to act as a man in the middle between the boiler and the remote controller. 

And now I am building a second version, more powerful, universal and for everybody to use!

How does it works?

Gas boiler and its remote controller communicates using OpenTherm protocol. It allows the boiler to send a lot of information about its state to the remote controller and allows remote controller to precisely control the temperature of hot water. Regulator acts as a gateway between the remote controller and boiler. It captures the data flowing between them and either uses hot water from accumulator tank or relay commands to the boiler to fulfill heating or domestic hot water demand. In addition, statistics can be captured.

Accumulator tank is equipped with a 3-way valve and heating pump to provide an accurate temperature for the heating system. The second pump runs water through a domestic hot water boiler. Both pumps and valve are controllers by the regulator. The regulator also reads 3 temperatures from accumulator tank (top, middle, bottom), temperature of heating water and return water to regulate 3-way valve.

Features:

  • Arduino compatible (MicroChip ATmega2561 microcontroller) 
  • built-in OpenTherm support - can act as a master, slave or gateway to boiler and thermostat 
  • 6 NTC temperature sensors (1 built-in) to monitor temperatures on various pipes and tanks 
  • water pressure sensor 
  • 3 high voltage relays to control pumps or boiler 
  • 3-way valve actuator control output 
  • Real-time clock 
  • ethernet connectivity 
  • WiFi connectivity 
  • NRF connectivity 
  • large display and rotary encoder as user interface 
  • 24V power supply (5V if OpenTherm is not used)

What is the status?

I am currently have a prototype ready to be coded and tested in my heating system.

5745c263-ff67-4a58-b55a-a7fe99f6765a.png

Schematic - microcontroller and auxiliaries

Portable Network Graphics (PNG) - 214.92 kB - 01/19/2019 at 08:28

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Portable Network Graphics (PNG) - 66.03 kB - 01/19/2019 at 08:28

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Portable Network Graphics (PNG) - 122.35 kB - 01/19/2019 at 08:28

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618fbbe9-fcb6-4026-9399-cf4f3f3e7d56.png

Schematic - Power Supply

Portable Network Graphics (PNG) - 41.94 kB - 01/19/2019 at 08:28

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  • OpenTherm Arduino shield

    Jiří Praus02/27/2019 at 16:56 0 comments

    I've got distracted a little bit with my Mechanical Tulip. No worries. I am working on this one right now. In the meantime, I've used my OpenTherm experience and knowledge to create an OpenTherm shield for Arduino UNO. It's an exact copy of OpenTherm component on this board. But can be used right away with any Arduino UNO board.

    It will allow you to control your boiler without a thermostat or act as a gateway between boiler and thermostat to monitor their activity! Now testing it. Will be soon available on my Tindie store.

  • Regulator electric schematics

    Jiří Praus01/20/2019 at 19:23 0 comments

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Discussions

George Fenyvesi wrote 10/01/2019 at 07:33 point

It seems to me that in the OpenTherm schematics the lower (slave in) optocoupler sides (I/O) has to be changed.

  Are you sure? yes | no

Jiří Praus wrote 10/01/2019 at 19:37 point

Oops, its still the old version with wrongly facing Optocoupler. Thanks for pointing that out! I am preparing update.

  Are you sure? yes | no

Jiří Praus wrote 10/01/2019 at 19:42 point

Fixed

  Are you sure? yes | no

dev wrote 07/26/2019 at 10:05 point

A highly promising project. I am looking at building an Opentherm Thermostat for my vacation home and would need to add the possibiliy to control via SMS text messages.  Do you think that would be an option easy enough to implement?

  Are you sure? yes | no

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